This invention relates to a novel polymer, to functionalized derivatives of said novel polymer, to processes for preparing said novel polymer and said derivatives and to compositions comprising said derivatives. More particularly, this invention relates to a modified elastomeric polymer, to functionalized derivates of said polymer, to processes for preparing said modified polymer and said functionalized derivatives and to compositions comprising said derivatives.
Elastomeric homopolymers and copolymers of various hydrocarbon monomers are, of course, well known in the prior art. For example, diolefin homopolymers are known to exhibit rubber-like characteristics while diolefin copolymers, particularly those comprising vinyl aromatic compounds, exhibit diversified characteristics ranging from rubber-like characteristics to resin-like characteristics, depending primarily upon the amount of diolefin branching, the amount of internal unsaturation incorporated by the diolefin and the content of the vinyl aromatic monomer in the copolymer. It is also known in the prior art to use polymers of this type and functionalized derivates thereof in various applications such as the molding of shoe soles and the like, as impact modifiers for various thermosetting resins, as adhesives, as sealants, in coating formulations, as binders and the like. As is also well known in the prior art, diolefin homopolymers and copolymers may be modified by incorporating one or more functional groups into the polymer, which functional groups will improve polymer properties for use in a variety of known areas of application. For example, it is known that: the incorporation of one or more mono- or polycarboxyl groups will improve the polymers adhesive properties, green strength and other properties; the incorporation of a silanol group will improve strength and friction properties; the incorporation of an ester group will improve the properties required in thermoset molding applications and the incorporation of phosphoric ester groups will improve the polymer's flame retarding characteristics.
Heretofore, several methods have been proposed for modifying various diolefin polymers to incorporate at least one functional group such as the functional groups disclosed in U.S. Pat. Nos. 3,135,716 and 4,409,357. These methods include the grafting of a dicarboxylic acid group or a derivative thereof onto a base polymer such as is taught in U.S. Pat. No. 4,329,430 and the grafting of mono- and polycarboxylic acid groups onto such a polymer as is taught in U.S. Pat. No. 4,579,429. These methods also include reaction of a functionalizing agent with a diolefin homopolymer or copolymer comprising at least one active group containing an alkali metal atom, particularly a lithium atom, as is taught in U.S. Pat. Nos. 3,135,716; 3,225,089; 3,242,129; 3,892,819 and 4,400,478. As is known in the prior art, these methods have led to the production of modified diolefin homopolymers and copolymers having improved properties for various applications. With the grafting methods, however, it is difficult to control the number of functional groups, such as carboxyl groups, actually incorporated into the polymer and, frequently, more carboxyl groups are incorporated than are necessary for the improvements sought. This, in turn, significantly increases the cost of the modified diolefin homopolymer or copolymer. Those methods wherein a functional group, such as carbon dioxide, is incorporated by reaction of a functionalizing agent with one or more active sites containing an alkali metal atom do not, on the other hand, suffer from these same disadvantages, however, it is, at best, difficult to control the number of functional groups, such as carboxyl groups, actually introduced into the polymer primarily because of the coupling reactions which frequently occur between the lithium salt groups formed as a result of the treatment with the functionalizing agent and the active sites themselves. In this regard, it is believed well known that a so called living polymer comprising at least one active site containing a lithium atom will react spontaneously with carbon dioxide to produce the lithium salt of an acid. The reaction may be represented as follows: EQU PS--PBD--Li--+CO.sub.2 .fwdarw.PS--PBD--CO.sub.2 Li
wherein PS--PBD is a block copolymer comprising a single block of polystyrene (PS) and a single block of polybutadiene (PBD). The lithium salt thus produced will then react with the living polymer. This reaction may be represented as follows: EQU PS--PBD--CO.sub.2 Li+PS--PBD--Li.fwdarw.(PS--PBD).sub.2 C=O+Li.sub.2 O
(PS--PBD--).sub.2 C=O is then a dicoupled polymer. This dicoupled polymer will also react with a living polymer to produce a tricoupled polymer. This reaction may be represented as follows: EQU (PS--PBD--).sub.2 C=O+PS--PBD--Li.fwdarw.(PS--PBD--).sub.3 C O Li
As is also well known, the dimer and trimer formed by the coupling reactions do not exhibit improved properties for various applications in which diolefin homopolymers and copolymers are normally used. For example, neither the dimer nor trimer contain the desired functional group, at least, not in an active form. Moreover, since the molecular weight is either doubled or tripled, the dimer and trimer are inferior to the base polymer without a functional group for use in most applications. In this regard, it should be noted that coupling significantly increases solution viscosity and when the polymer is to be used as a solution the higher viscosity will reduce, if not eliminate, the range of equipment that might otherwise be used for such applications. It will, of course, be appreciated that similiar reactions could be illustrated for other functionalizing reagents as shown in the aforementioned U.S. Patents and similar adverse effects would be realized.
In processes proposed heretofore for carboxylating diolefin homopolymers and copolymers, the yield of uncoupled polymer containing carboxyl functionality has, generally, been less than 10 wt% of the total product. Moreover, the use of coupling inhibitors such as methanol has not significantly changed the yield of uncoupled polymer containing carboxyl functionality even though these inhibitors do significantly reduce the amount of coupled product actually obtained. In light of this, then, the need for an improved process for functionalizing diene homopolymers and copolymers, which process will permit control of the amount of functionality actually incorporated into the polymer and prevent, or at least permit control of, coupling is believed to be readily apparent. In addition, the need for an improved polymer containing various functionality is also believed to be readily apparent.